Many studies have shown that we can easily recognize objects without the aid of vision. In this application we propose to study how the size and shape of objects that we grasp in our hands are represented in the cortex. Our working hypothesis is that size and shape perception involves the integration of cutaneous receptors in the skin with proprioceptors in the skin, muscles and joints. The cutaneous receptors provide information about the local features of the object such as the form, texture and whether it is moving. The proprioceptors provide information about hand conformation and tell the nervous system where the cutaneous inputs are located in 3D space. There are three aims. The first is to investigate how cutaneous and proprioceptive input related to object shape is integrated in somatosensory cortex. The second is to investigate how the size of objects are represented in cortex. The third aim is to investigate how size and shape are processed in animals performing discrimination tasks. For the first two aims we will perform psychophysical experiments on humans performing shape or size discrimination tasks. In addition, we will perform single-unit recordings from both primary and secondary somatosensory cortex from awake-behaving animals. In these studies the animals' hand and fingers will be passively moved to contact objects of varying size and shape. In the third aim animals will perform two-alternative force choice tasks where they are required to discriminate either the size or the shape of objects. In this study we will investigate the mechanisms of selective attention and in addition will test whether these neurons are directly related to perception using electrical stimulation to alter behavior. These studies will provide an understanding of the mechanisms of shape processing in the somatosensory cortex and an understanding of how hand conformation is represented. The study has direct relevance to the development of sensory feedback for amputees with upper-limb prosthetics. PUBLIC HEALTH RELEVANCE: These studies have important implications for using electrical feedback in amputees with upper limb prosthetics. In recent years we have made remarkable progress in controlling prosthetic arms with signals taken directly from the motor cortex. However our ability to provide sensory feedback has been limited to targeted reinnervation of receptors in the arm are moved to the skin on the chest or to simple vibratory feedback. Providing realistic perception of inputs from a prosthetic arm is a major challenge. In these studies we will determine whether electrical stimulation can be used to produce the percepts of object size and shape.